1. Technical Field
The invention relates to an electro-acoustical device and, more particularly, to a folded horn loudspeaker for reproducing low frequency audible sound at high output levels from electric-acoustic transducers having relatively small diaphragms.
2. Description of the Problem
The reproduction of low frequency audible sound, with high fidelity and at high intensity levels, poses a number of challenges. To do so from a small, energy efficient package, portable enough to be moved and suitable for open air use is especially difficult. Generally, high output, high efficiency, low frequency loudspeakers have been built around a horn. A horn is in effect an acoustic transformer, allowing the designer to obtain the output performance of a driving unit having a large area diaphragm from a unit having a smaller area diaphragm while minimizing cone/diaphragm resonance issues that exist with direct radiator devices. Increasing the effective diaphragm area renders radiation impedance increasingly resistive with the result that increasing power is radiated at the desired low frequencies. However, increasing acoustic power output from most horn designs has required increasing diaphragm piston travel in order to move the required volume velocity of air. Piston travel becomes an important limiting factor relating to the amount of power that can be delivered to the horn.
Another limitation on the total energy input that can be introduced to a horn has been the limited scalability of horns. Though examples of multiple driver horns are known, typically only a single driving unit for a given frequency range has been provided. One example of a multiple driver horn (U.S. Pat. No. 5,898,138) positions a pair of low frequency transducers having throats located equidistant from the horn's mouth. While effective such an arrangement is still not readily scalable.